1. Field of the Invention
The present invention relates to an exhaust muffler.
2. Description of Background Art
An exhaust muffler is known wherein a partition wall is provided between expansion chambers with a communicating tube passing through the partition wall so as to provide communication between the expansion chambers. See, for example, Japanese Patent Application Laid-Open Publication No. 2006-207548. The communicating tube is a double tube formed of an outer communicating tube and an inner communicating tube. An inside passage within the inner communicating passage and an annular passage between the inner communicating tube and the outer communicating tube are formed as exhaust passages through which exhaust gases flow in opposite directions to each other. With this construction, in comparison with the case where a plurality of communicating tubes are arranged spaced apart from each other, an arrangement space for the plurality of communicating tubes (exhaust passages) is suppressed.
In the above mentioned exhaust muffler, an end portion of the inner communicating tube located in one end portion of the double communicating tube facing into one of the expansion chambers extends beyond a distal end opening of the outer communicating tube with both of distal end openings of the inner communicating tube and the outer communicating tube being located close to each other. The distal end opening of the inner communicating tube functions as an intake and exhaust port (an exhaust port in Japanese Patent Application Laid-Open Publication No. 2006-207548) of the inside passage, and the distal end opening of the outer communicating tube functions as an intake and exhaust port (an exhaust port in Japanese Patent Application Laid-Open Publication No. 2006-207548) of the annular passage. More specifically, an outlet of the outer communicating tube and an inlet of the inner communicating tube are directed in the same direction, and the inlet of the inner communicating tube is located in the exhaust direction of the outlet of the outer communicating tube, so that the exhaust gas flowing out of the outlet of the outer communicating tube easily enters the inlet of the inner communicating tube before it is expanded enough within the expansion chamber. Therefore, there is a possibility that the volume of the expansion chamber is not sufficiently utilized.